<template>
  <div>
    <router-link to="/"
                 class="header-abs"
                 v-show="showAbs"
                 tag="div">
      <div class="iconfont header-abs-back">&#xe624;</div>
    </router-link>
    <div class="header-fixed"
         v-show="!showAbs"
         :style="showStyle">
      <router-link to="/">
        <div class="iconfont header-fixed-back">&#xe624;</div>
      </router-link>景点详情</div>
  </div>
</template>

<script>
export default {
  name: 'DetailHeader',
  data () {
    return {
      showAbs: true,
      showStyle: {
        opacity: 0
      }
    }
  },
  methods: {
    handleScroll () {
      const top = document.documentElement.scrollTop
      if (top > 60) {
        let opacity = top / 140
        opacity = opacity > 1 ? 1 : opacity
        this.showStyle = {
          opacity
        }
        this.showAbs = false
      } else {
        this.showAbs = true
      }
    }
  },
  activated () {
    window.addEventListener('scroll', this.handleScroll)
  },
  deactivated () { // 在转到其他页面或者这个页面被替换的时候调用
    window.removeEventListener('scroll', this.handleScroll)
  }
}
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl'
// 图标其实相当于一段文本,设置行高和父级元素高度相同,它就可以垂直居中,设置text-align:center,就可以水平居中
.header-abs
  position absolute
  top 0.2rem
  left 0.2rem
  width 0.8rem
  height 0.8rem
  line-height 0.8rem
  text-align center
  border-radius 0.4rem
  background rgba(0, 0, 0, 0.8)
  .header-abs-back
    color #fff
    font-size 0.4rem
.header-fixed
  z-index 2
  position fixed
  top 0
  left 0
  right 0
  overflow hidden // 文本占据了一行,把箭头挤到了横条下面,又因为设置的overflow,所以看不见了要设置绝对定位才能看到
  height $headerHeight
  line-height $headerHeight
  text-align center
  background $bgColor
  color #fff
  font-size 0.32rem
  .header-fixed-back
    position absolute
    left 0
    top 0
    width 0.64rem // 宽度
    font-size 0.4rem
    color #fff
</style>
